A total of 16 CFS/POTS and 20 control subjects underwent graded tilt table testing (at 0, 15, 30, 45, 60 and 75 degrees) with continuous cardiovascular, cerebrovascular, and respiratory monitoring and neurocognitive testing using an n-back task at each angle.

Subject dropout due to orthostatic presyncope [faintness] at each angle was similar between groups.

• There were no n-back accuracy or RT (reaction time) differences between groups while supine [lying down].

• CFS/POTS subjects responded less correctly during the n-back task test and had greater nRT (normalized RT) at 45, 60 and 75 degrees.

• Furthermore, at 75 degrees CFS/POTS subjects responded less correctly and had greater nRT than controls during the 2-, 3- and 4-back tests.

• Changes in cerebral blood flow velocity (CBFV) were not different between the groups and were not associated with n-back task test scores.

Thus we conclude that increasing orthostatic stress combined with a cognitive challenge impairs the neurocognitive abilities of working memory, accuracy and information processing in CFS/POTS, but that this is not related to changes in cerebral blood flow velocity.

Individuals with CFS/POTS should be aware that orthostatic stress may impair their neurocognitive abilities.